Thermophysical properties for binary mixtures epsilon-caprolactam + 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and cyclohexanone oxime + 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide have been measured. New measurements of heat capacity for caprolactam (CL) in the temperature range of (260 to 370) K and parameters of fusion have been carried out. Mutual solubility of caprolactam (CL) and 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([HMIM][NTf2]) in the wide concentration range and solubility of cyclohexanone oxime (CHO) in [HMIM][NTf2] within x(CHO) from (0.2 to 1) were studied by a visual method. Activity coefficients of the components were estimated. Vapor-liquid equilibrium (VLE) of the binary mixture CL + [HMIM][NTf2] was studied using the Knudsen method. VLE measurements were carried out over the broad concentration range at temperatures between (315.3 and 331.9) K. Activity coefficients of CL in [HMIM][NTf2] have been determined from the VLE data and are described formally by using the NRTL equation. Activity coefficients in infinity dilution of CL in [HMIM][NTf2] have been derived by extrapolation to the infinite dilution of CL. Activity coefficients at infinite dilution of CHO in the temperature range (364.9 to 438.0) K and CL at 427.5 K in [HMIM][NTf2] have been determined by gas chromatography using the ionic liquid as the stationary phase.